where \({Q}_{A}\)  and \(F^{\mu }_{A}\)  represent the energy and momentum transfer rate, respectively, relative to \(U^{\mu }_{A}\) . Likewise, to the first order
\(F^{\mu }_{A}={\mathrm { \bf a}}^{-1}(0,\partial ^{i}f_{A})\)  where \(f_{A}\)  is a momentum transfer potential and \(\bar{Q}_{A}\)  represents the interaction term.
From Eqs. (REF ) and (REF ), we find [1]}
\(Q^{A}_{0}=-{\mathrm {\bf a}}\left[\bar{Q}_{A}(1+\phi )+\delta {Q_{A}}\right],\quad Q^{A}_{i}={\mathrm {\bf a}}\partial _{k}\left[f_{A}+\bar{Q}_{A}v\right],\) 
